Let's have an LED driving module so that we can output different patterns for

status indications etc.

led.h

@@ -0,0 +1,11 @@
+/* led.h */
+
+#include "timer.h"
+
+typedef unsigned int led_pattern;
+
+extern led_pattern led_pattern_active[];
+
+void led_set(bool on);
+void led_update(void);
+void led_set_pattern(led_pattern *pattern);